Method for making sintered body with metal powder and sintered body prepared therefrom

ABSTRACT

The present invention relates to a metal powder sintered body by using fine powders as the raw material and the fabrication method thereof. The sintered body has a characteristic composition including iron (Fe), carbon (C), nickel (Ni) and at least one strengthening element, in the ratios as follows: Ni: 3.0-12.0%, carbon: 0.1-0.8%, the strengthening element: 0.5-7.0%, and the remaining portion being Fe. The sintered body has high tensile strength, high hardness, and good ductility, without treatment with the quenching process.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefits of Taiwan applicationserial no. 93116634, filed Jun. 10, 2004, and no. 93126297, filed Sep.1, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a sintered body andfabrication method thereof. More particularly, the present inventionrelates to compositions of sinter-hardening powders, the sintered bodyby using fine powders as raw materials, and the fabrication methodthereof.

2. Description of Related Art

As is well known in the art, the design of the alloy of powdermetallurgy is always the critical starting point for the development ofpowder metallurgy. By combining different alloying elements anddifferent amounts of additives, various alloy steels can be developedand applicable to diversified circumstances. In general, powdermetallurgy components are required to possess mechanical propertiessuitable for their application fields. Thus, hardening thermal processeslike quenching followed by tempering are normally applied to thesintered components in order to obtain the desirable mechanicalproperties.

However, while the quenching is performed, several problems likedeformation, size inconsistency, or cracking after quenching may becaused by the fast cooling procedure. In addition, the thermal processesperformed on the components will cause additional costs. Therefore,sinter-hardening powders have been developed, by adding highhardenability alloying elements such as molybdenum (Mo), nickel (Ni),manganese (Mn) or chromium (Cr) to iron powders, then pressing out thegreen compact through the conventional compacting process and thensintering the green compact, with the hardness above HRC30. Examples ofalloys produced by this method are Ancorsteel 737SH(Fe-0.42MN-1.40Ni-1.25Mo—C) from Hoegananes Corp. and ATOMET 4701(Fe-0.45Mn-0.90Ni-1.00Mo-0.45Cr—C) from Quebec Metal Powders Limited.The components made from these powders are cooled at rates of a minimumof 30° C. per minute in the sintering furnace to generate martensite andbainite.

Although the alloying elements in these sinter-hardening components arestill not homogenized completely using the regular sintering conditionsof 1120° C. and 30-40 minutes, these sinter-hardening powders providebetter mechanical properties than those possible using nonsinter-hardening powders. Although sinter-hardening powders can reducecosts due to the elimination of the quenching process, a high coolingrate system has to be installed in the sintering furnace. Furthermore,the aforementioned cooling rates, while slower than quenching, are stillfast enough to cause problems such as deformation, inconsistency of thedimensions, and even cracking. According to U.S. Pat. No. 5,682,588, theclaimed powders are compacted by the conventional pressing process,sintered between 1130-1230° C., and then cooled at rates of 5-20°C./minute in order to reach the desired sinter-hardening effects. Thishas improved the process by lowering the minimum cooling rate of 30°C./min, as described in the previously mentioned processes. However, themechanical properties, in particular, the ductility, are stillunsatisfactory.

Concerning the press-and-sinter process, there are standards (the Year2003 version) for sinter-hardening alloys set forth by the Metal PowderIndustries Federation (MPIF). FLNC-4408 (1.0-3.0% Ni, 0.65-0.95% Mo,1.0-3.0% Cu, 0.6-0.9% C, and the remaining portion is Fe) is the examplewith the best mechanical properties. After sinter-hardening andtempering, the above-mentioned alloy can reach a tensile strength of 970MPa under the density of 7.2 g/cm³, and the hardness can reach HRC30,while the ductility is only 1.0%. Although this press-and-sintered alloybelongs to one of the sinter-hardening type alloys, its mechanicalproperties are still not satisfactory.

In the field of powder metallurgy, fine powders are commonly used in themetal injection molding process. In contrast, the powders used in thetraditional powder metallurgy process (e.g. press-and-sinter process)are much coarser. The particle size of the powders used in metalinjection molding is usually less than 30 μm, while the particles usedin the press-and-sinter process are under 150 μm in size. Since thediffusion distances in fine powers are shorter, the added alloyingelements can be homogenized more easily in the matrix materials.Therefore, components sintered from the fine powders possess mechanicalproperties better than those of the traditional press-and-sinteredcomponents.

At present, the alloys commonly used for metal powder injection moldingare the Fe—Ni—Mo—C alloy series, exemplified by MIM-4605 (1.5-2.5Ni,0.2-0.5% Mo, 0.4-0.6% C, <1.0% Si, the remaining portion is Fe), whichhas the best mechanical properties according to the MPIF standards. Thisalloy, after sintering, reaches a tensile strength of 415 MPa, ahardness of HRB62, and a ductility of 15%. In order to attain the bestmechanical properties, the sintered product has to be heat-treated(quenched and tempered). It then reaches a tensile strength of 1655 MPa,a hardness of HRC48, and a ductility of 2.0%.

Although excellent mechanical properties of the metal injection moldedproducts can be obtained by heat treatment after sintering, the costs ofthe heat treatment accounts for a large part of the whole productioncost. Hence, it is critical to lower the costs of the heat treatment,for example, by using sinter-hardening materials. However, according tothe Metal Powder Industries Federation Standards, no sinter-hardeningalloys are listed for the metal injection molding process.

As mentioned above, application of fine powders improves homogenizationof the alloying elements and mechanical properties of the products.However, application of fine powders in the traditional press-and-sinterprocess is difficult because of the poor flowability of the powder,which in turn makes it difficult to fill the powders into the diecavity, and thus automated pressing can not be used. However, thisproblem can be overcome by granulating the fine powders into largespherical particles, and the granulated powders can then be applied inthe press-and-sinter process.

REFERENCE PAPERS

-   U. Engström, J. McLelland, and B. Maroli, “Effect of    Sinter-Hardening on the Properties of High Temperature Sintered PM    Steels”, Advances in Powder Metallurgy & Particulate materials-2002,    Compiled by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I.    Sanderow, MPIF, Princeton N.J., 2002, part 13, page 1-13.-   K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K. Kanto,    “Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a carbon/carbon    Composite Mesh Belt Furnace”, Advances in Powder Metallurgy &    Particulate materials-2002, Compiled by V. Arnhold, C-L Chu, W. F.    Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J., 2002, part    13, page 14-22.-   H. Suzuki, M. Sato, and Y. Seki, “Sinter Hardening Characteristics    of Ni—Mo—Mn—Cr Pre-Alloyed Steel Powder”, Advances in Powder    Metallurgy & Particulate materials-2002, Compiled by V. Arnhold, C-L    Chu, W. F. Jandeska, Jr., and H. I. Sanderow, MPIF, Princeton N.J.,    2002, part 13, page 83-95.-   D. Milligan, A. Marcotte, J. Lingenfelter, and B. Johansson,    “Material Properties of Heat Treated Double Pressed/Sintered P/M    Steels in Comparison to Warm Compacted/Sinter Hardened Materials”,    Advances in Powder Metallurgy & Particulate materials-2002, Compiled    by V. Arnhold, C-L Chu, W. F. Jandeska, Jr., and H. I. Sanderow,    MPIF, Princeton N.J., 2002, part 4, page 130-136.-   B. Lindsley, “Development of a High-Performance Nickel-Free P/M    Steel”, K. Kanno, Y. Takeda, B. Lindqvist, S. Takahashi, and K. K.    Kanto, “Sintering of Prealloy 3Cr-0.5Mo Steel Powder in a    carbon/carbon Composite Mesh Belt Furnace”, Advances in Powder    Metallurgy & Particulate materials-2004, Compiled by W. B. James,    and R. A. Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page    19-27.-   B. Hu, A. Klekovkin, D. Milligan, U. Engström, S. Berg, and B.    Maroli, “Properties of High-Density Cr—Mo Pre-alloyed Materials    High-Temperature Sintered”, Advances in Powder Metallurgy &    Particulate materials-2004, Compiled by W. B. James, and R. A.    Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 28-40.-   P. King, B. Schave, and J. Sweet, “Chromium-containing Materials for    High-Performance Components”, Advances in Powder Metallurgy &    Particulate materials-2004, Compiled by W. B. James, and R. A.    Chernenkoff, MPIF, Princeton N.J., 2004, part 7, page 70-80.-   M. Schmidt, P. Thorne, U. Engström, J. Gabler, T. J. Jesberger,    and S. Feldbauer, “Effect of Sintering Time and Cooling Rate on    Sinter Hardenable Materials”, Advances in Powder Metallurgy &    Particulate materials-2004, Compiled by W. B. James, and R. A.    Chernenkoff, MPIF, Princeton N.J., 2004, part 10, page 160-171.-   MPIF Standard 35, Materials standards for Metal Injection Molded    Parts, 2000 edition, MPIF, Princeton N.J., pp. 12-13.-   MPIF Standard 35, Materials standards for P/M Structural Parts, 2003    edition, MPIF, Princeton N.J., pp. 46-47.-   K. S. Hwang, C. H. Hsieh, and G. J. Shu, “Comparison of the    Mechanical Properties of Fe-1.75Ni-0.5Mo-1.5Cu-0.4C Steels made from    the PIM and the Press-and-Sinter Processes”, Powder Metallurgy,    2002, Vol. 45, No. 2, pp. 160-166.-   U.S. Pat. No. 5,876,481, 1999.-   U.S. Pat. No. 5,834,640, 1998.-   U.S. Pat. No. 5,682,588, 1997.-   U.S. Pat. No. 5,476,632, 1995.

SUMMARY OF THE INVENTION

The present invention is directed to a metal powder sintered body, byusing a new composition and by using fine powers as the raw material.The particle size of the powders is between 0.1˜30 μm. The sintered bodyfabricated has a high hardenability and the sintered body can attainexcellent mechanical properties under the normal cooling rate (3-30°C./minute) inside the traditional sintering furnace.

In accordance with one aspect of the present invention, a metalinjection molding fabrication method is provided, by using the newcompositions of the sinter-hardening metal powders in the conventionalmetal injection molding process. The sintered compact can be treatedwith low temperature tempering, without quenching, to obtain excellentmechanical properties.

In accordance with another aspect of the present invention, a powdermetallurgy fabrication method is provided by using the new compositionsof the sinter-hardening metal powders in conventional powder metallurgyprocesses (press-and-sinter process). The sintered compact can betreated with low temperature tempering, without quenching, to obtainexcellent mechanical properties.

According to the above-mentioned and the other purposes of the presentinvention, a metal powder sintered body is provided, by using finepowders as the raw material with the sintered body containing thecharacteristic composition including iron (Fe), carbon (C), nickel (Ni),and at least one other strengthening element, in the ratios as follows:Ni: 3.0-12.0%, carbon: 0.1-0.8%, the strengthening elements: 0.5-7.0%,and the remaining portion is Fe. The above-mentioned strengtheningelements can be selected from the group consisting of Molybdenum (Mo),Chromium (Cr), Copper (Cu), Titanium (Ti), Aluminum (Al), Manganese(Mn), Silicon (Si), and Phosphorous (P). The element carbon mentionedabove can be provided by adding graphite or using carbon-containingcarbonyl iron powders. The sintered body of the above-mentioned powdershas a tensile strength of over 1450 MPa, a hardness of over HRC38, and aductility of over 1% without the use of any quenching process.

According to the above-mentioned and the other purposes of the presentinvention, a metal injection molding fabrication method is provided. Theabove-mentioned compositions of the sinter-hardening metal powders canbe applied to metal injection molding. The method comprises providingthe powders and binders, while the diameters of elemental or alloyedpowders are 0.1˜30 μm. The above-mentioned powders and binders arehomogenously kneaded to form a feedstock. The green compacts are thenmolded from the feedstock using the injection molding machine. Thebinders in the above-mentioned green compacts are removed using thewell-known solvent or thermal debinding methods. The debound body issintered and cooled at a cooling rate of 3-30° C./minute in thesintering furnace, which can be a regular furnace, such as a vacuumfurnace or a continuous pusher furnace. The process after sintering isthe low temperature tempering process with the tempering temperatureranging from 150-400° C. and the time ranging from 0.5-5 hours, toimprove the mechanical properties of the sintered body.

According to the above-mentioned and the other purposes of the presentinvention, a powder metallurgy method using the above-mentionedcompositions of the sinter-hardening metal powders into powdermetallurgy processes (press-and-sinter process) is provided. The methodcomprises providing the powders and binders, whereas elemental powdersor alloying powders have diameters ranging from 0.1˜30 μm. Then thepowder granulation process is performed to allow the powders and bindersto bind into round granules. Thereafter, the above round granules aresieved in order to select appropriate particles with good flowabilityfor the compacting machine. The green compact is obtained by filling theparticles into the die cavity, and this is followed by compacting theparticles under high pressures. The binder in the above mentioned greencompact is removed during the debinding process. After the debindingprocess, the body is sintered in the sintering furnace, which can be acommon furnace, such as a vacuum furnace or a continuous pusher furnace.The cooling rate can range from 3-30° C./minute. The post-sinteringprocess is the low temperature tempering process with the temperatureranging from 150-400° C. and the time ranging from 0.5-5 hours toimprove the mechanical properties of the sintered body. It is noted thatthe granulated powders in combination with the sinter-hardening alloyingredients from the present invention and with the press-and-sinterprocesses can obtain components with excellent mechanical propertieswithout the quenching process.

According to the above, the present invention provides a formulation forthe fine sinter-hardening type powders, applicable to the metalinjection molding process or traditional powder metallurgy process(press-and-sinter process) so as to produce the sintered body (workpiece) of high strength, high density, high hardness, and highductility, with a lower production cost.

It is to be understood that the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and they are incorporated in andconstitute a part of this specification. The drawings illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 is a cross-sectional view of the sample in example 1, observingthe ductile microstructure with dimple type fractures by the scanningelectronic microscope.

DESCRIPTION OF THE EMBODIMENTS

The foregoing descriptions of specific embodiments of the invention havebeen presented for purposes of illustration and description. They arenot intended to be exhaustive or to limit the invention to the preciseforms disclosed. Obviously, many modifications and variations arepossible in light of the above teaching. The embodiments were chosen anddescribed in order to explain the principles and the application of theinvention, thereby enabling others skilled in the art to utilize theinvention in its various embodiments and modifications according to theparticular purpose intended. The scope of the invention is intended tobe defined by the claims appended hereto and their equivalents.

The element ingredients and the mechanical properties of the sinteredbody are listed in Table 1 and Table 2, whereas examples 1-4 in Table 2are the sintered bodies made from the metal injection molding process;examples 5-6 are the sintered body made from the traditional powdermetallurgy process. Table 1 and Table 2 are used to illustrate thesintered body elements and the fabrication method for the presentinvention, while examples 1-6 represent the present invention andexamples A-D are used as the comparison group according to the availableliteratures.

EXAMPLE A

According to the standards from the MPIF-35, the elements of MIM-4605used in injection molding are shown in Table 1, while the mechanicalproperties of the sintered body produced by the elements of MIM-4605 areshown in Table 2.

EXAMPLE B

Same composition as in example A. After the heat treatment, productsimprove enormously in terms of mechanical properties, as shown in Table2.

EXAMPLE C

According to the MPIF-35 standards, the elements of MIM-2700 used ininjection molding are shown in Table 1, while the mechanical propertiesof the sintered body produced by the elements of MIM-2700 are shown inTable 2.

EXAMPLE D

According to the MPIF-35 standards, the elements of sinter-hardeningalloy FLNC-4408 used in the traditional press-and-sinter process areshown in Table 1, while the mechanical properties of the sintered bodyproduced by the elements of FLNC-4408 are shown in Table 2.

EXAMPLE 1

Following Table 1, the required powders with particle sizes ranging from0.1˜30 μm are mixed together with 7 wt % of the binder, mixed in the Ztype high shear rate mixer at 150° C. for 1 hour, then cooled to roomtemperature to obtain the granulated feedstock. Thereafter, thepreviously mentioned granulated feedstock is filled into the injectionmolding machine to produce the tensile test bar (e.g. the standardtensile bar from the MPIF-50 standard.). The tensile bar is de-boundunder the procedure applied from the known arts in the industry, forexample, debinding for five hours using heptane as the solvent at 50°C., then heating the tensile bar in the vacuum furnace from the roomtemperature up to 650° C. at a rate of 5° C./minute, raising thetemperature to 1200° C. at a rate of 10° C./minute, sintering at 1200°C. for two hours, and then cooling to room temperature, so as to reach ahardness of HRC51 and a ductility of 1.0%. The tensile bar, after beingtempered at 180° C. for two hours, reaches a tensile strength of 1800MPa, a hardness of HRC45, and a ductility of 3%, as shown in Table 2.FIG. 1 is a fracture surface of the sample in example 1. The ductilemicrostructure with dimple type fractures is observed using a scanningelectronic microscope. This indicates that products of high hardness,high tensile strength, and high ductility can be produced from thesealloying elements. Take the as-sintered MIM-4605 as an example, which isan injection molding material with the best mechanical properties listedby the MPIF. The properties are 415 MPa, HRB62, and 15% ductility, asshown in example A in Table 2. After quenching and tempering, theimproved MIM-4605 will possess 1655 MPa, HRC48, and a ductility of 2%,as shown in example B in Table 2. MIM-4605 needs to be quenched andtempered to reach the mechanical properties similar to those made by thepresent invention. However, the sintered body of the present inventionpossesses good mechanical properties without the need for quenching.

EXAMPLE 2

The same processes as in example 1 but with the compositions listed inexample 2 in Table 1. After tempering, the tensile bar has a tensilestrength of 1780 MPa, a hardness of HRC-45, and a ductility of 4%.

EXAMPLE 3

The same processes as in example 1, but with the compositions listed inexample 3 in Table 1. After tempering, the tensile bar has a tensilestrength of 1720 MPa, a hardness of HRC-46, and a ductility of 4%.

EXAMPLE 4

The same processes as in example 1, but with the compositions listed inexample 4 in Table 1. After tempering, the tensile bar has a tensilestrength of 1450 MPa, a hardness of HRC-28, and a ductility of 4%.

EXAMPLE 5

Following the compositions listed in example 5 in Table 1, the powdershaving particle sizes ranging from 0.1˜30 μm and the required componentsare mixed together with 1.5 wt % of the binders. The powders, water, andbinders (e.g.: Polyvinyl alcohol) are blended into a slurry. The slurryis then atomized from the nozzle at high speed and dried by hot air orhot nitrogen to evaporate the water within. The fine powders are thusbonded with each other by the binder to form granulated powders withgood flowability. The particle size of the graduated powder is about 40μm. The previously mentioned granulated powders are filled into the diecavity to produce the green tensile bar by the automatic compactingmachine. The tensile bar is de-bound under the procedure applied fromthe known arts in the industry. For example, the temperature will beraised at the rate of 5° C./minute up to 400° C., and then at the rateof 3° C./minute up to 1100° C., maintained for one hour, and then raisedat the rate of 10° C./minute up to 1200° C., and sintering will continueat this temperature for one hour. Afterwards, the tensile bar is cooledas the temperature of the furnace drops, and the tensile bar is temperedfor 2 hours at 180° C. without the use of the quenching process. Asshown in the Table 2, the tensile bar has a tensile strength of 1690MPa, a hardness of HRC47, and a ductility of 3%. Compared to FLNC-4408(the best sinter-hardened press-and-sinter work piece listed by theMPIF), FLNC-4408 has 970 MPa, HRC30, and 1% ductility, as shown inexample D in Table 2.

EXAMPLE 6

The process is the same as in example 5, but with the compositions asshown in example 6 in Table 1. After 2 hours of tempering at 180° C.,the tensile bar possesses a tensile strength of 1650 MPA, a hardness ofHRC43, and a ductility of 4%. TABLE 1 Commonly used percentages andelements for the examples 1-6 in the present invention and for cases A-Dfrom the industry and based on the Metal Powder IndustriesFederation(MPIF)standards (weight percentage, wt %) Element Ex: 1 Ex: 2Ex: 3 Ex: 4 Ex: 5 Ex: 6 Ex: A& B Ex: C Ex: D C 0.36%  0.34%  0.4% 0.45% 0.5% 0.4% 0.4-0.6% <0.1% 0.6-0.9% Ni 8.0% 9.0% 8.0% 4.5% 8.0% 7.5%1.5-2.5%  6.5-8.5%   1.0-3.0% Mo 0.8% 0.8% 1.0% 1.0% 0.8% 0.8% 0.2-0.5%<0.5% 0.65-0.95%  Cr 0.8% 0.8% 0.8% 0.5% 0.8% 0.5% — — — Mn 0.6% — — — —— — — — Cu — — 1.5% — 0.5% —. — — 1.0-3.0% Si 0.3% 0.3% 0.3% 0.3% 0.3%0.3% <1.0 <1.0 — Fe the rest the rest the rest the rest the rest therest the rest the rest the rest

TABLE 2 Comparison of mechanical properties of the alloys among examples1-6 and examples A-D Tensile Density Quench-hardening strength DuctilityEx: (g/cm3) process (MPa) Hardness (%) A 7.5 None 415 HRB62 15 B 7.5Yes* 1655 HRC48 2 C 7.6 None 440 HRB69 26 D 7.2 None** 970 HRC30 1.0 17.6 None** 1800 HRC45 3 2  7.6. None** 1780 HRC45 4 3 7.6 None** 1720HRC46 4 4 7.5 None** 1450 HRC38 5 5 7.5 None** 1690 HRC47 3 6 7.5 None**1650 HRC43 4*Austenizied at 860° C. and then oil quenched, then tempered at 180° C.for 2 hours.**Sintered and then tempered at 180° C. for 2 hours.

In conclusion of the above description, compared to the best injectionmolding alloy, MIM-4605 (after quenching and tempering), and the bestsinter-hardening alloy, FLNC-4408, for the press-and-sinter work piece,listed by the Metal Powder Industries Federation (MPIF); thesinter-hardening alloy of the present invention can attain similar oreven better mechanical properties without the quench-hardening process.Besides, the problems derived from quench-hardening in the prior art,including deformation, inconsistency of the dimensions, and crackingafter quenching, etc, can be avoided in the present invention, and thecosts from the quench-hardening process can be eliminated. Althoughsinter-hardening alloys are available for the pressing process intraditional powder metallurgy, the cooling rate required for thesintered body is much higher than that required in this study. Thesintered body of the present invention provides excellent mechanicalproperties, and it also provides advantages in the areas of dimensionalcontrol and lower costs.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the structure of the presentinvention without departing from the scope or spirit of the invention.In view of the foregoing, it is intended that the present inventioncover modifications and variations of this invention provided they fallwithin the scope of the following claims and their equivalents.

1. A metal powder sintered body by using fine powders as a raw material,and an alloy of the sintered body comprising: Iron (Fe), Carbon (C),Nickel (Ni) and at least one strengthening element, wherein the alloyincludes 3.0-12.0% nickel, 0.1-0.8% carbon, and 0.5-7% the strengtheningelement, while a remaining portion of the alloy is iron, and diametersof the fine powders range from 0.1-30 μm.
 2. The sintered body asrecited in claim 1, the strengthening element is selected from the groupconsisting of Molybdenum (Mo), Chromium (Cr), Copper (Cu), Titanium(Ti), Aluminum (Al), Manganese (Mn), Silicon (Si), and Phosphorous (P).3. The sintered body as recited in claim 1, wherein a source of carbonis from graphite.
 4. The sintered body as recited in claim 1, wherein asource of carbon is from carbonyl iron powder.
 5. The sintered body asrecited in claim 1, wherein the sintered body has a tensile strengthover 1400 MPa, a hardness over HRC35, and a ductility over 1%.
 6. Amethod for fabricating the sintered body as recited in claim 1,comprising: providing powders and binders; kneading the powders and thebinders, so that the powders and the binders mix into a homogenousfeedstock; performing an injection molding process so as to dischargethe feedstock to obtain a green compact; debinding the green compact toremove the binders in order to form a body; sintering and cooling thebody in a sintering furnace; and performing a post-sintering thermalprocess.
 7. The method as recited in claim 6, wherein the powders areelemental powders or prealloyed powders with diameters ranging from0.1˜30 μm.
 8. The method as recited in claim 6, wherein the sinteringfurnace is a vacuum furnace or a continuous furnace.
 9. The method asrecited in claim 6, wherein sintering conditions for the sintered bodyinclude a sintering temperature of 1100-1350° C. for 0.5-5 hours, and acooling rate of 3-30° C./minute.
 10. The method as recited in claim 6,wherein the post-sintering thermal process is a low temperaturetempering process, with a tempering temperature ranging from 150-400° C.for 0.5-5 hours.
 11. The method as recited in claim 6, wherein thesintered body has a tensile strength over 1400 MPa, a hardness overHRC35, and a ductility over 1%.
 12. A method for fabricating thesintered body as recited in claim 1, comprising: providing powders andbinders; performing a powder granulation process so that the powders andthe binders are joined into round granules; sieving the round granulesto select granules with a predetermined flowability for a compactingmachine; performing a compacting process by filling the granules in adie cavity and pressing them out, so as to generate a green compact;debinding the green compact to remove the binders to form a body;sintering and cooling the body inside a sintering furnace; andperforming a post-sintering thermal procedure.
 13. The method as recitedin claim 12, wherein the powders are elemental powders or prealloyedpowders with diameters ranging from 0.1˜30 μm.
 14. The method as recitedin claim 12, wherein the sintering furnace is a vacuum or a continuousfurnace.
 15. The method as recited in claim 12, wherein sinteringconditions for the sintered body include a sintering temperature of1100-1350° C. for 0.5-5 hours, and a cooling rate of 3-30° C./minute.16. The method as recited in claim 12, wherein the post-sinteringthermal process is a low temperature tempering process, with a temperingtemperature ranging from 150-400° C. for 0.5-5 hours.
 17. The method asrecited in claim 12, wherein the sintered body has a tensile strengthover 1400 MPa, a hardness over HRC35, and a ductility over 1%.